1. Field of the Invention
This invention relates generally to the cooling of electronic circuitry, integrated circuit boards, heat sinks, and power electronic components to increase their power density. Most electrically energized equipment is limited in its capacity by thermal constraints. The advent of more electric vehicles such as ships, transportation equipment including cars, trucks, aircraft and trains has pushed the capabilities of many electronic controls to their maximum thermal constraints These constraints have a direct effect on efficiency, power density, packaging and the architectural configuration for these components in their operating environments.
Each year additional software and hardware is required by electronic systems in order to meet customer expectations, particularly in power electronics. Increasingly there are many applications where significantly higher power is required and space is at a premium. Efficiency and power density may be compromised by the addition of more cumbersome traditional integrated circuit cooling systems utilizing cold plates and traditional spray cooling methods. There are many applications where this is not a significant issue, however, there are an increasing number of environments, such as with power electronics where power density must be optimized to enable such applications to be commercialized.
One such example is the current interest in the introduction of hybrid/electric propulsion systems in transportation. Power density is a critical factor in determining overall fuel efficiency of the platform. It is critical to reduce an electrical component""s size to achieve lightweight, cost-effective components.
The present invention relates to a significantly more effective method and apparatus for the removal of latent heat from integrated circuit boards, heat sinks, electric coils, integral power busses and their components. I have found that a significant increase in power density is achieved by utilizing the integrated circuit board and/or their components and/or associated heat sinks as the injection source in the spray cooling process. By cooling electronic components in accordance with the principles of the invention, two significant factors are accomplished. In the first, the heat is more effectively removed directly from the source of the heat generated. This helps to eliminate any unnecessary high and low pressure regions integral to the environment in which the components are encased. The second factor is the elimination of additional manifolds and injectors to nebulize liquids which add to a system""s complexity, requires more space, adds additional cost and increases the relative amount of maintenance.
2. Description of Related Art
U.S. Pat. No. 5,719,444 discloses a packaging and cooling system for one or more semi-conductor devices in which an evaporative type liquid coolant is sprayed from a plurality of spray nozzles onto the semi-conductor devices and the liquid is then condensed, cooled and recirculated by a pump to an input plenum for reuse in a closed circuit.
U.S. Pat. No. 5,880,931 discloses a spray cooled circuit card cage which includes a manifold to provide coolant fluid to a plurality of spray plate assemblies which direct the spray of coolant over the top surface of the electronic cards within the card cage.
U.S. Pat. No. 4,392,153 discloses a semi-conductor electronic device which is attached to fluid cooled heat sinks to provide efficient removal of heat generated by the device.
U.S. Pat. No. 4,573,067 discloses a semi-conductor chip which is provided with fins to provide improved heat dissipation capability.
U.S. Pat. No. 5,23 9,200 discloses a heat transfer module which is placed into thermal contact with a chip on a circuit board for conducting heat therefrom. The heat transfer module has a channel therein for receiving a coolant.
U.S. Pat. No. 5,345,107 discloses a cooling apparatus for an electronic device in which a cooling body is placed into surface contact with an electronic device.
U.S. Pat. No. 5,049,973 discloses a heat sink for electrical components.
U.S. Pat. No. 5,373,417 discloses a liquid cooled circuit package where the package is filled with a cooling liquid during operation.
U.S. Pat. No. 3,746,947 discloses a semi-conductor device which is positioned with an enclosure which has liquid coolant circulating therein.
None of the foregoing prior art suggested ports, perforations or passageways in the circuit board, the components themselves, the heat sinks, or the conductive leads for the components to promote internal cooling of the components by conduction, and cooling of the surface of the components by evaporative and conductive cooling.
The present invention provides a method and apparatus for addressing a significant obstacle in increasing power density of integrated circuit boards and their components during the spray cooling process. Many features, embodiments and principles of the present invention are disclosed in U. S. patent application Ser. No. 091465,428 entitled Method and Apparatus for Increasing the Power Density of Integrated Circuit Boards and Their Components filed on Dec. 21, 1999. That application and all is contents and disclosures are hereby incorporated herein by reference.
Substantial inefficiencies occur in traditional systems that attempt to remove heat from energized circuit board components. One traditional system is the spray cooling process. In that system nozzles or injectors typically are placed adjacent to a board in the proximity of the energized components. The nozzles or injectors spray nebulized cooling fluid down onto the circuit board and its components. The cooling fluid then evaporates removing heat from the circuit board and its components. In the typical closed loop system, the vapor must be collected, condensed, and circulated back to the nozzles or injectors.
In the present invention, cooling fluid is supplied to passageways within an integrated circuit board and/or its components and/or heat sinks. The fluid passes through the passageways and exits through ports or nozzles on the surface of the integrated circuit board, components or heat sink. Thus, the components may be cooled by both conductive cooling as the fluid passes through the core of the component, circuit board, or heat sink and by evaporative cooling as the liquid changes phase at or near the surface of the component, circuit board, or heat sink.
More traditional spray-cooling designs have to overcome a multitude of obstacles. These obstacles are a result of trying to direct coolants towards, as opposed to away from, the energized components on an integrated circuit board. This results in unnecessary increased boundary layers and vortices during phase change. This is due to vapors having to escape the area where the fluid vaporized directly in opposition to the direction of the spray pattern during the cooling process. Thus, the heat removal in the traditional spray-cooling process is less efficient than in the present invention. It should be emphasized that this invention may provide for some of its coolants to reach the board in liquid form, however, significant advantages are accomplished by using the integrated circuit board as the source of the cooling fluid. The net effect is increased power density.
Thermal instabilities can create mechanical fatigue over time particularly, in high power density applications where temperatures may vary significantly from one location in a component as compared to another. This is becoming a common occurrence in cold plate cooling creating separations or fractures and is avoided in the utilization of the subject invention. The core of a component maintains a more consistent temperature as does the outer surface while employing the principles of this invention. On a micro-prospective, dissimilar temperatures also inhibit the free passage of electrons which is ultimately a function of increased resistance and affects the overall efficiency and equilibrium in an integrated circuit board and its components Thermal inconsistencies and mechanical instabilities may also result in increased audible/radiated and electrical noise in addition to fatigue.
One embodiment of the present invention can be carried out in a manner where a continuous supply of liquid coolants are provided to an integrated circuit board, a heat sink, a pair of boards set back-to-back, or a board set back-to-back with a heat sink. When two boards are set back-to-back, sufficient space may be provided between the two boards to provide a chamber for the introduction of coolants. The peripheral edges of the boards are joined and sealed creating a void or chamber within a sandwich-like enclosure to allow the two boards to act as an intake manifold for liquid coolants. Boards may be dielectrically isolated or conductively connected to one anther through the surrounding attachments making up the enclosure. The choice would depend on whether each board has similar or dissimilar power requirements. If power requirements are dissimilar, the boards must be dielectrically isolated or have an appropriate stepper. Power supplies, microprocessors, SCR""s, IGBT""s, voltage steppers, invertors, rectifiers, surge capacitors, batteries, or regulators may be strategically placed on these surfaces between the two boards.
Alternatively, such components may be individually mounted to a manifold adapted to supply cooling fluid to the components.
The present invention also may be used to increase the efficiency of heat sinks. As with the other applications of the invention, a heat sink is provided with internal passages through which cooling fluid is passed. The passages end at a port or nozzle on the surface of the heat sink. Cooling fluid may be supplied to the heat sink by way of a manifold or by placing the heat sink back-to-back with a circuit board. The peripheral edges of the board and heat sink are joined and sealed creating a void or chamber within a sandwich-like enclosure to act as an intake manifold for liquid coolants.
An additional alternate embodiment of the invention is the attachment of a manifold to the bottom of a single integrated circuit board or heat sink utilizing the board or heat sink to provide at least one surface an enclosed fluid chamber. Alternatively, such a manifold could be attached to a single component such as a transformer.
The inlet chamber between the boards or the board and the heat sink or the intake manifold enables the introduction of the liquid through openings in components mounted thereto and/or through openings in the board or the heat sink itself. If desired, a nozzle or nozzles may be connected to perforations in the board or heat sink to direct cooling fluid onto specific components. Alternatively, ports or nozzles may be positioned above the surface of the board to allow cooling fluid to be sprayed down onto components mounted on the board. Regulation of the openings is managed by the size and placement of perforations or inlets relative to cooling requirements in the system""s architecture. Generally, the closer a component is to an inlet, the larger the intake delivery port that is required to provide adequate pressure to that component. Conversely, the further a component is located from the inlet, the smaller the intake delivery port that is necessary to maintain adequate pressure. This design mimics a biological capillary design. It provides for better interaction of the liquid, electron and gas exchange allowing for the component""s substrates to act as a membrane like our skin thus, more closely mimicking a biological system such as that found in the human body.
Yet, another way to visualize this micro-port configuration, from a turbulence perspective, is to more closely emulate the design of a feather. This design also helps to evacuate vapor directing it towards the cooling source. This is a result of continually homogenizing respectively large vortices and reducing their size and increasing acceleration when the gas stream approaches the vapor exit of the chamber and exits to the cooling source. The cooling source in some cases may be the enclosure itself of these components. The placement of high heat components such as power supplies, magnetics, SCR""s and IGBT""s or transformers near the inlet side of the board may also help the natural acceleration of vapor to the cooling source. This design also helps to evacuate vapor directing it towards the cooling source.
This results in a reduction of unnecessary vortices. When two boards are placed back-to-back, it allows the mounting of components on both sides of what becomes a single integrated circuit board with an internal fluid filled chamber. The liquid can be directed away from an integrated circuit board effectively in any direction in this configuration. It is therefore an object of the present invention to provide methods and apparatus for increasing the effectiveness of the spray cooling for integrated circuit boards, their components, and heat sinks.
It is an additional object of the invention to provide for effectively cooling the conductive source and the integrated circuit board from within and on the surface. This increases the overall carrying capacity of the conductive infrastructure, including the buss, by providing a more uniformed temperature with a simple more unified transition of heat removal.
It is still an additional object of this present invention to improve the power density of the components attached to and utilized as an integral part of an injection manifold where the components themselves contain internal passages and perforations thus, rendering them all part of a fully integrated injection and nebulizing system.
The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood from the following detailed description of the preferred embodiments when taken in conjunction with the following drawings. It should be understood, however, that the detailed description and the specific examples while representing the preferred embodiments are given by way of illustration only and should not be construed in a limiting sense.